The present invention relates to a chuck for machine tools, such as lathes and cylindrical grinders, for chucking workpieces having a large diameter or a large length.
For example when a diametrically large or an elongated workpiece is to be machined by turning at an end portion or joint portion thereof, the workpiece must be attached to a chuck while being supported in suspension by a chain block or the like to center the portion of the workpiece to be machined.
The portion to be machined, if eccentric with the portion to be held by the clamp jaws of the chuck, is extremely difficult to center, necessitating much labor and time for chucking.
Further because conventional automatic chucks are so constructed that the clamp jaws are radially movable in a concentric arrangement, they are useful insofar as the portion of the workpiece to be chucked is concentric or in alignment with the portion thereof to be machined, but if otherwise, it is almost impossible to use such a chuck, or the workpiece must be centered by a very cumbersome procedure.
U.S. Pat. No. 3,338,120 discloses a thread cutting machine wherein the workpiece can be chucked as centered with eccentricity corrected. U.S. Pat. No. 3,630,535 granted Dec. 28, 1971 discloses a chuck for machine tools wherein clamp means concentric with the axis of rotation of three jaws is adapted to move three other jaws for correcting the eccentricity of a workpiece.